1. Field
Described here is an article for magnetic heat exchange and methods of manufacturing it.
2. Description of Related Art
The magnetocaloric effect describes the adiabatic conversion of a magnetically induced entropy change to the evolution or absorption of heat. Therefore, by applying a magnetic field to a magnetocaloric material, an entropy change can be induced which results in the evolution or absorption of heat. This effect can be harnessed to provide refrigeration and/or heating.
Magnetic heat exchange technology has the advantage that magnetic heat exchangers are, in principle, more energy efficient than gas compression/expansion cycle systems. Furthermore, magnetic heat exchangers are environmentally friendly, as ozone depleting chemicals such as CFC's are not used.
Magnetic heat exchangers, such as that disclosed in U.S. Pat. No. 6,676,772, typically include a pumped recirculation system, a heat exchange medium such as a fluid coolant, a chamber packed with particles of a magnetic refrigerant working material which displays the magnetocaloric effect, and a means for applying a magnetic field to the chamber.
In recent years, materials, such as La(Fe1-aSia)13, Gd5(Si,Ge)4, Mn(As,Sb) and MnFe(P,As) have been developed which have a Curie Temperature, Tc, at or near room temperature. The Curie Temperature translates to the operating temperature of the material in a magnetic heat exchange system. Consequently, these materials are suitable for use in applications such as building climate control, domestic and industrial refrigerators and freezers, and automotive climate control.
Further developments of these materials have been directed towards optimizing the composition so as to increase the entropy change and to increase the temperature range over which the entropy change occurs. This enables smaller applied magnetic fields to be used to achieve sufficient cooling and a stable refrigeration cycle to be achieved over a larger temperature range. These measures aim to simplify the design of the heat exchange system as the smaller magnetic fields can be produced by a permanent magnet rather than requiring an electromagnet or even a superconducting magnet. However, further improvements are desirable to enable a more extensive application of magnetic heat exchange technology.